Misfire after rev limiter

[dan7301]

Just brought my new jeep home to MN from Denver, now begins the fun of learning all about it.
The previous owner mentioned he put new plugs and a coil onto it to try curing a misfire.
On the way home at about 2am I saw a fire half a mile down a gravel road. Whipped around a hammered it, in case it was a accidental. It was just a big brush pile.
But I think the kick down is too tight, because it hit the Rev limiter in first for half a second before I lifted.
After it shifted it was misfiring and limited to 3k rpm. I hooked up the scanner and it gave me p0300, p0302, p0305, and p0352.
Looking at it, cylinders 2 and 5 are twinned, so they would be on the same coil pack, wasting spark every other. Seems like the 352 caused the others.
Turning the rig off for 5 minutes didn't do anything, but unhooking the battery for a minute fixed it.
I plan on pulling the coil and looking at the plugs, not trusting the PO to have done it right, but is there anything else I should be looking at? Could the ecu have "forgotten" to come out of Rev limit on that coil?

 

[dan7301]

Just brought my new jeep home to MN from Denver, now begins the fun of learning all about it.
The previous owner mentioned he put new plugs and a coil onto it to try curing a misfire.
On the way home at about 2am I saw a fire half a mile down a gravel road. Whipped around a hammered it, in case it was a accidental. It was just a big brush pile.
But I think the kick down is too tight, because it hit the Rev limiter in first for half a second before I lifted.
After it shifted it was misfiring and limited to 3k rpm. I hooked up the scanner and it gave me p0300, p0302, p0305, and p0352.
Looking at it, cylinders 2 and 5 are twinned, so they would be on the same coil pack, wasting spark every other. Seems like the 352 caused the others.
Turning the rig off for 5 minutes didn't do anything, but unhooking the battery for a minute fixed it.
I plan on pulling the coil and looking at the plugs, not trusting the PO to have done it right, but is there anything else I should be looking at? Could the ecu have "forgotten" to come out of Rev limit on that coil?

Wasn't sure if filling the profile added it as a signature, info here:

It's a 2001 Sahara with the 4.0 and a 3 speed auto.

180k miles. Using a little coolant but there's no contamination so I'm not worried there.

 

[macleanflood]

Only thing I would add to that is a Mopar crank position sensor. I chased random misfires forever and finally replaced my CPS and solid ever since.

Ask me how I know not to trust a single sensor the PO replaced on my Jeep. That being said... don't fire the parts cannon at it either...I've gotten a few Napa Echlins to work and folks have great luck with Standard Motor Products.

-Mac

 

[dan7301]

The fact it was a light switch for those 2 cylinders before and after definitely makes me think it's a digital signal of some sort, not an intermittent like a weak spark.

 

[JKP]

The coolant use is probably a cracked head on your 01.

Wide open throttle will expose a weak coil. Just go out and accelerate hard and see if the misfires come back.

 

[dan7301]

The coolant use is probably a cracked head on your 01.

Wide open throttle will expose a weak coil. Just go out and accelerate hard and see if the misfires come back.

Is there a sure way to verify a cracked head or no without pulling the head? How does the crack normally present? 400 miles in was the last time I looked at the oil and there's no milkshake or anything. Does it leak into the intake and steam clean a cylinder?

Edit: Also, I've had it wot a fair amount, but I lifted around 4500 rpm to let it shift. I forgot to while looking at the fire, so it hit the rev limiter and those cylinders just shut off like a light bulb.

 

[JKP]

Remove the oil cap, look straight down at the head with the engine hot. It usually cracks and leaks there.

You can also sample the oil and send it off for analysis.

On my YJ, which just has a single coil, when it would get weak, the engine would just quit under WOT. Let off the gas and it would fire up.

 

[dan7301]

Cool, I've got some research to do.

Thanks for the pointers, I'll come back if I find anything.

 

[dan7301]

I checked the jeeps oil after I got home on my motorcycle and it's about a quart over full. Not a good sign to start.

Pop the oil cap and fire it up....

I don't think you can get any more proof of a cracked head.
When I first got it to my friends house, about 20 minutes from the point of purchase, I added about a quart of coolant to the radiator. So it's maybe been leaking a while. What are the odds my cross country trek messed up the bottom end? The oil on the dipstick doesn't have any sparkles in it.

 

[JKP]

Yep, time for a new head.

What's the oil pressure look like?

 

[dan7301]

Yep, time for a new head.

What's the oil pressure look like?

It never dropped below 40 on the gauge, so plenty good.

 

[JKP]

You're probably OK then. If the bearings were wiped out, you'd have low pressure.

You can get a test gauge and screw it in the sender's port for a more accurate measurement if you want.